A substance
that blocks a type of enzyme called a kinase. Human cells
have many different kinases, and they help control
important functions, such as cell signaling, metabolism,
division, and survival. Certain kinases are more active in
some types of cancer cells and blocking them may help keep
the cancer cells from growing. Kinase inhibitors may also
block the growth of new blood vessels that tumors need to
grow. Some kinase inhibitors are used to treat
cancer.